xfs: pull up stack_switch check into xfs_bmapi_write

The stack_switch check currently occurs in __xfs_bmapi_allocate,
which means the stack switch only occurs when xfs_bmapi_allocate()
is called in a loop. Pull the check up before the loop in
xfs_bmapi_write() such that the first iteration of the loop has
consistent behavior.
Signed-off-by: NBrian Foster <bfoster@redhat.com>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NBen Myers <bpm@sgi.com>

fs/xfs/xfs_bmap.c

@@ -4680,9 +4680,6 @@ __xfs_bmapi_allocate(
 			return error;
 	}
 
-	if (bma->flags & XFS_BMAPI_STACK_SWITCH)
-		bma->stack_switch = 1;
-
 	error = xfs_bmap_alloc(bma);
 	if (error)
 		return error;
@@ -4956,6 +4953,9 @@ xfs_bmapi_write(
 	bma.flist = flist;
 	bma.firstblock = firstblock;
 
+	if (flags & XFS_BMAPI_STACK_SWITCH)
+		bma.stack_switch = 1;
+
 	while (bno < end && n < *nmap) {
 		inhole = eof || bma.got.br_startoff > bno;
 		wasdelay = !inhole && isnullstartblock(bma.got.br_startblock);